Re: 24-hour vs. 12-hour time, ambiguity, and abbreviations (was Re: Default date output format changed after an upgrade to buster)

[David Wright <deblis@lionunicorn.co.uk>]

On Thu 12 Sep 2019 at 23:14:52 (-0400), The Wanderer wrote:
> On 2019-09-12 at 21:49, David Wright wrote:
> > On Thu 12 Sep 2019 at 12:42:01 (-0400), The Wanderer wrote:
> >> On 2019-09-12 at 12:03, David Wright wrote:
> 
> >>> It might be ambiguous if m were also an abbreviation for midnight,
> >>> which I've never come across.
> >> 
> >> Neither have I, but I also haven't come across any *other* abbreviation
> >> for it which might be used in this type of context (have you?), and "M"
> >> is just as intuitive a choice for abbreviating "midnight" as it is for
> >> abbreviating "meridiem".
> >> 
> >> One could argue "M" for "midnight" and "N" for "noon", but then you lose
> >> the intuitiveness of M for meridiem, and people would mishear the two as
> >> each other in nonline conversation all the time anyway.
> > 
> > I don't see a need for a one-letter abbreviation for midnight, nor the
> > wisdom in introducing one that's already used in the same context.
> > Where would you use it?
> 
> Wherever you need to specify midnight in a form where specifying any
> other time would get the "AM"/"PM"/"M"(eridiem) abbreviation.
> 
> To have a two-letter abbreviation for midnight but a one-letter one for
> noon might be acceptable, although it would feel lopsided to me, but
> just offhand I don't know of any suitable candidate to be that
> two-letter abbreviation. Again, do you have any suggestions?

No: I'm the one suggesting it's neither desirable nor needed.
So "Wherever you need to" doesn't help.

> > Why not just drop 12-hour times? I don't think I've ever formatted a
> > 12-hour time on a computer (unless you want to count the example
> > quoted below).
> 
> This isn't limited to the context of "on a computer". I think I
> originally came up with the notion of referring to noon as "12:00 M" in
> a context of mentioning the times in out-loud conversation; the
> abbreviations are certainly used in more than just computerized contexts.
> 
> For myself, I likely would drop 12-hour time. But as long as the world
> isn't agreeing to do that, pursuing ways to make 12-hour time work more
> logically and less ambiguously is still worthwhile.

Oh, don't misunderstand me. I'm not arguing against using 12-hour time
in ordinary conversation and in "real life". I've produced scores of
tickets, posters and programmes with 12-hour times, and wouldn't dream
of designing one that advertised a concert at 18:30 rather than 6.30 pm.
I don't design posters with output generated by a date command, but if
that became a necessity through sheer quantity, I would use
date +'%l.%M %P', sure (but I'd add a test for 12).

> And of course part of the reason I like the idea is because I find the
> odd looks I get when I refer to "12:00 M" without previous explanation
> to be amusing.
> 
> >>> When I read emails, I only see the Date: line from the header, and
> >>> the timedates used in the quotation lines. One thing I find odd is
> >>> mixing AM/PM with hours containing a leading zero. I was always
> >>> taught that 7 p.m. or 7pm was not written as 07, but I see that a
> >>> lot here. Contrast
> >>> 
> >>> $ TZ=Europe/Paris date +'%I.%M %p'
> >>> 06.01 PM
> >>> $ TZ=Europe/Paris date +'%l.%M %p'
> >>>  6.01 PM
> >>> $ 
> >> 
> >> That's probably to ease parsing by automated tools, such as sort, so
> >> that they don't have to worry about handling field width.
> > 
> > That wouldn't be possible anyway, because you don't have control over,
> > for example, whether the time follows the date, and other variability.
> 
> That just makes it even harder; not impossible, but unwieldy and
> problematic enough that very few are likely to bother with trying.
> 
> > No. I think it's more likely that most people don't notice
> > conventions unless they're brought to their attention. Of course, if
> > you're old enough, you had years of pre-digital experience when no
> > one thought of padding dates and times with 0s. That might be why I
> > notice 'odd' formatting like this.
> 
> I may be confused. I thought we were talking about why some people /
> tools use zero-padded hours fields with 12-hour time; I don't see how
> the decision to do that could in any way arise from failure to notice a
> convention without having it pointed out.

I don't think they make a conscious *decision* to use leading zeroes,
they just use the same old %I rather than %_I (≡ %l) because they
hadn't thought about it, and their output didn't jar.

Conventional:   8 pm    9 pm   10 pm   11 pm
Casual:        08 pm   09 pm   10 pm   11 pm

I've omitted the minutes so that the jarring effect might be more obvious.

When reading fully specified times, with minutes and seconds, I think
an experimental psychologist would be able to show that a leading zero
fools the brain into parsing the time in 24-hour clock mode, and then
the am/pm at the end causes reparsing, which slows comprehension.
Perhaps it wouldn't work like that in America; I don't know.

Cheers,
David.